Operation Castle - Background

Background

Bikini Atoll had previously hosted nuclear testing in 1946 as part of Operation Crossroads where the world’s fourth and fifth atomic weapons were detonated in Bikini Lagoon. Since then, US nuclear weapons testing had moved to Eniwetok Atoll to take advantage of generally larger islands and deeper water. Both Atolls were part of the US Pacific Proving Grounds.

The extremely high yields of the Castle weapons caused concern within the AEC that potential damage to the limited infrastructure already established at Eniwetok would delay other operations. Additionally, the cratering from the Castle weapons was expected to be comparable to that of Ivy Mike, a 10.4 megatons of TNT (Mt) device tested at Eniwetok in 1952 leaving a crater approximately 1 mile (1.6 km) in diameter marking the location of the obliterated test island Elugelab.

The Ivy Mike test was the world's first "hydrogen bomb", producing a full-scale thermonuclear or fusion explosion. The Ivy Mike device used liquid deuterium, an isotope of hydrogen, making it a "wet" bomb. The complex dewar mechanisms needed to store the liquid deuterium at cryogenic temperatures made the device three stories tall and 82 tons in total weight, far from being a deliverable weapon. With the success of Ivy Mike as proof of the Teller-Ulam bomb concept, research began on using a “dry" fuel to make a practical fusion weapon so that the United States could begin production and deployment of thermonuclear weapons in quantity. The final result incorporated lithium deuteride as the fusion fuel in the Teller-Ulam design, vastly reducing size and weight and simplifying the overall design. Operation Castle was charted to test four dry fuel designs, two wet bombs, and one smaller device. Approval for Operation Castle was communicated to JTF-7 by Major General Kenneth D. Nichols, General Manager of the AEC, on 21 January 1954.